This application relates generally to electrical power generation and, more specifically, to the estimation of the consumed battery life and/or remaining battery life of a battery used in a wind energy application.
A utility-scale wind energy system or wind farm includes a group of wind turbines that operate collectively as a power plant to produce electrical energy without the consumption of fossil fuels. The output of wind energy from a particular wind turbine or wind farm is less consistent than the energy output from fossil fuel-fired power plants. As a result, the power from wind turbines operating at nominal conditions in a wind farm may not meet output requirements for the power plant. For example, the power from a power plant may not track the power forecast due to forecast errors. As another example, the rate of power production for a power plant may be outside of a desired range because of wind gusts. A conventional approach for dealing with these and other similar situations is to use controls to manage the operation of the wind farm, such as utilizing pitch control of the rotor blades to increase or decrease the power produced by the individual wind turbines.
Traditional utility-scale wind energy systems are not dispatchable sources of electricity that can be cycled on or off at the request of power grid operators. For that reason, a wind farm may include an energy storage device, such as one or more rechargeable batteries, that is linked to the power grid and that may assist with meeting requirements on the power production by the power plant. When energy demand peaks, the wind turbines of the wind farm will sink energy directly into the grid. When energy demand is diminished, excess energy from the wind turbines may be stored in the energy storage device and later discharged upon demand to alleviate any deficits in output requirements for the power plant.
The pattern of charge and discharge cycles for intermittent generators, such as wind turbines, may be irregular. Nevertheless, a battery experiencing on average a single daily charge and discharge for twenty years in a wind farm accumulates roughly 7,300 cycles. As a result, candidate batteries used in wind farms must be characterized by long cycle lifetimes. Battery life is dependent on both the depth of discharge and the rate of discharge, as well as other factors such as temperature, charging strategy, etc.
Accurate estimation of remaining battery life (RBL) may be important for batteries used in energy storage applications for wind energy. For example, knowledge of the RBL may find use in making appropriate adjustments to control strategies for the battery such that battery life is greater than the lifetime of the wind farm. As another example, knowledge of the RBL may be useful is in the context of battery monitoring and prognostics for the purposes of scheduling battery maintenance or replacements.
The estimation of remaining battery life and optimally sizing batteries is a difficult proposition. To determine remaining battery life, a determination must first be made of the consumed battery life. Typically, manufacturers may supply battery life data that indicates the projected number of cycles to failure as a function of the depth of discharge. However, the direct use of manufacturer-supplied battery life data may lead to gross errors in battery lifetime estimation, when the battery is used in a wind farm, due to the highly irregular pattern of charging and discharging. These gross errors may result in either a higher system cost than necessary or the specification of an undersized battery prone to premature failure.
Improved techniques are needed for estimating the consumed battery life and, therefore, the remaining battery life of a battery used in a wind farm application.